The overall objective of this proposal is to determine temporal and spatial relationships existing between anatomically and functionally related neurons in the developing orbitofrontal and motor cortices, neostriatum and thalamus of the puppy. Both light microscopic silver degeneration and autoradiographic methods will be used to investigate the sequence of axonal development of neurons in these regions. Horseradish peroxidase methods will be employed to determine cell types giving rise to specific terminal projection fields. The Golgi method will be used to study the rates of dendritic and somatic maturation of these neurons and the relationship of this development to the arrival of afferent fibers. Standard transmission electron microscopy as well as combined electron microscopic and Golgi-electron microscopic methods will be used to determine the precise temporal and spatial parameters of synaptogenesis in these regions. These data will all be compared to connectivity patterns found in the mature dog.